1. Field of the Invention
This invention relates to the art of mold manufacturing and specifically to the manufacturing of molds that are to be used integrally with the casting material with which they are filled.
2. Description of the Prior Art
The manufacture of molds for the purpose of casting is a well known technology. Most commonly, a mold is used to form a casting material, such as metal, concrete, or plastic into a specified shape. The casting material is introduced into the mold in a fluid form and is allowed to set, thereby assuming the shape of the mold.
In most instances, a mold is a tool for forming casting material into a predetermined shape that is separated from the set casting material and either discarded or used again. For this reason, molds commonly are concave. This shape facilitates separation of the mold from the casting material.
In certain instances, however, the mold and the casting material are intended to be used integrally. In this instance, a concave mold may have shortcomings. The mold and the casting material may separate unintentionally, frustrating the performance of the integrated mold and casting material.
It is therefore desirable, in instances where the mold and the casting material are to be used integrally, to have a mold with at least one surface which exerts pressure on the set casting material such that the set casting material remains biased into the mold.
It is also often desirable to have the mold made of the least expensive, substantially rigid material available. Commonly, the material that is best suited for this purpose is plastic. Plastic is usually formed by injection molding, which is also a well known art. Injection molding requires a mold into which fluid hot thermoplastic is injected. After a suitable cooling period, the plastic is then removed from the exterior mold. Such injection molding is used to produce plastic structures that are concave on one surface and convex on the opposite surface. This is so because injection molding generally requires an injectible mold formed of two movable plates. The first of these plates has a concave portion, the second of these plates has a slightly smaller convex portion that fits approximately into the concave portion of the first plate. The two portions are separated by a gap that defines the injectible mold. The first and second plates are concave and convex, respectively, because the resulting plastic must separate easily from the plates. No current technology exists that provides for an injection molded plastic mold created from a single piece that has a surface that would retain set casting material within the mold.